Pretty much what the others said. Personally, I'm not overly fond of Amazon and their business strategy, so I avoid their products. For e-books, especially, I prefer to be as independent as possible, and I don't want to have to jailbreak a device to be able to use it the way I'd like. I buy books from indie vendors like XinXii and Smashbooks, and disinfect stuff I purchase in the iBooks store (during the times when it is possible), and it all lives inside Calibre to be put on the devices I want to read something on.
I guess if none of those aspects matter to you, Amazon and a Kindle are a great choice. They do have the largest selection of books and the hardware is both solid and inexpensive. For me, though, the iPad is all the "boxing myself in" I'm willing to do.
